Canola oil seed protein isolates having protein contents of at least 100 wt % (N×6.25) can be formed from oil seed meal by a process as described in copending U.S. patent application Ser. No. 10/137,391 filed May 3, 2002 (U.S. patent application Publication No. 2003-0125526 and WO 02/089597) and U.S. patent application Ser. No. 10/476,230 filed Jun. 9, 2004 (U.S. patent application Publication No. 2004-0254353), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference. The procedure involves a multiple step process comprising extracting canola oil seed meal using an aqueous salt solution, separating the resulting aqueous protein solution from residual oil seed meal, increasing the protein concentration of the aqueous solution to at least about 200 g/L while maintaining the ionic strength substantially constant by using a selective membrane technique, diluting the resulting concentrated protein solution into chilled water to cause the formation of protein micelles, settling the protein micelles to form an amorphous, sticky, gelatinous, gluten-like protein micellar mass (PMM), and recovering the protein micellar mass from supernatant having a protein content of at least about 100 wt % (N×6.25). As used herein, protein content is determined on a dry weight basis. The recovered PMM may be dried.
In one embodiment of the process, the supernatant from the PMM settling step is processed to recover canola protein isolate from the supernatant. This procedure may be effected by initially concentrating the supernatant using an ultrafiltration membrane and drying the concentrate. The resulting canola protein isolate has a protein content of at least about 90 wt %, preferably at least about 100 wt % (N×6.25).
The procedures described in U.S. patent application Ser. Nos. 10/137,391 and 10/476,230 are essentially batch procedures. In copending U.S. patent application Ser. No. 10/298,678 filed Nov. 19, 2002 (U.S. patent application Publication No. 2004-0039174 and WO 03/043439), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a continuous process for making canola protein isolates. In accordance therewith, canola oil seed meal is continuously mixed with an aqueous salt solution, the mixture is conveyed through a pipe while extracting protein from the canola oil seed meal to form an aqueous protein solution, the aqueous protein solution is continuously conveyed through a selective membrane operation to increase the protein content of the aqueous protein solution to at least about 50 g/L, while maintaining the ionic strength substantially constant, the resulting concentrated protein solution is continuously mixed with chilled water to cause the formation of protein micelles, and the protein micelles are continuously permitted to settle while the supernatant is continuously overflowed until the desired amount of PMM has accumulated in the settling vessel. The PMM is recovered from the settling vessel and may be dried. The PMM has a protein content of at least about 90 wt % (N×6.25), preferably at least about 100 wt %. The overflowed supernatant may be processed to recover canola protein isolate therefrom, as described above.
Canola seed is known to contain about 10 to about 30 wt % proteins and several different protein components have been identified. These proteins include a 12S globulin, known as cruciferin, a 7S protein and a 2S storage protein, known as napin. As described in copending U.S. patent application Ser. No. 10/413,371 filed Apr. 15, 2003 (U.S. patent application Publication No. 2004-0034200 and WO 03/088760) and U.S. patent application Ser. No. 10/510,766 filed Apr. 29, 2005 (US Patent Application Publication No. 2005-0249828), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, the procedures described above, involving dilution of concentrated aqueous protein solution to form PMM and processing of supernatant to recover additional protein, lead to the recovery of isolates of different protein profiles.
In this regard, the PMM-derived canola protein isolate has a protein component content of about 60 to about 98 wt % of 7S protein, about 1 to about 15 wt % of 12S protein and 0 to about 25 wt % of 2S protein. The supernatant-derived canola protein isolate has a protein component content of about 60 to about 95 wt % of 2S protein, about 5 to about 40 wt % of 7S protein and 0 to about 5 wt % of 12S protein. Thus, the PMM-derived canola protein isolate is predominantly 7S protein and the supernatant-derived canola protein isolate is predominantly 2S protein. As described in the aforementioned U.S. patent application Ser. Nos. 10/413,371 and 10/510,766, the 2S protein has a molecular size of about 14,000 daltons, the 7S protein has a molecular mass of about 145,000 daltons and the 12S protein has a molecular size of about 290,000 daltons.
There has previously been described in Krzyzaniak et al in Nahrung (42) 1998, Nr. 3/4, p. 201-204, the purification to homogenity of the 2S storage protein napin from rape seed and characterization of the secondary structure and conformation stability of the protein. The napin was isolated by extraction from rape seeds with buffer A (50 mM NaH2PO4, pH 7.0, 1 mM EDTA), followed by precipitation using (NH4)2SO4, dissolution of the resulting pellet in buffer A, dialysis against the same buffer and desalting by gel chromatography using a Sephadex G-50 column. Fractions containing napin extract were collected and re-precipitated with (NH4)2SO4. The resulting crude napin was dissolved in buffer B (buffer A at pH 7.4), dialyzed against it, then loaded on to a CM-Sephadex C-50 column and eluted with a gradient of 0.15 to 0.35 M NaCl in buffer B. Fractions containing napin were pooled, precipitated with (NH4)2SO4, redissolved in buffer A and dialyzed. Napin was further purified by cation exchange HPLC using gradients up to 1 M NaCl at pH 5.0. The fractions with λmax=280 nm were collected, concentrated and analyzed.
The applicants are aware of additional literature references describing the laboratory preparation of samples of 2S canola protein, purified to homogeneity, as follows:                Berot, S., Compoint, J. P., Larre, C., Malabat, C. and Gueguen, J. 2005. Large scale purification of rapeseed proteins (Brassica napus L). J. Chromatography B, 818: 35-42.        Bhatty, R. S., McKenzie, S. L. and Finlayson, A. J. 1968. The proteins of rapeseed (Brassica napus L.) soluble in salt solutions. Can. J. Biochem., 46:1191-1197.        Gehrig, P. M., Krzyzaniak, A., Barciszewski, J. and Biemann, K. 1996. Mass spectrometric amino acid sequencing of a mixture of seed storage proteins (napin) from Brassica napus, products of a multigene family. Proc. Natl. Acad. Sci. U.S.A., 93: 3647-3652.        Monsalve, R. I. and Rodriguez, R. 1990. Purification and characterization of proteins from the 2S fraction from seeds of the Brassicaceae family. J. Exper. Bot., 41(222): 89-94.        Muren, E., Ek, B., Bjork, I. and Rask, L. 1996. Structural comparison of the precursor and the mature form of napin, the 2S storage protein in Brassica napus. Eur. J. Biochem., 242: 214-219.        
The novel canola protein isolates provided herein are distinguished from such disclosures in that the 2S predominated canola protein isolates provided herein always comprise a small quantity of 7S protein.
Canola is also known as rapeseed or oil seed rape.